Sudden loss of spark - please help

[500dollar744ti]

I'm away from home with my boat -1990 MCM 350 Magnum- and while navigating an inlet, the engine just cut off. I quickly tried to restart, and nothing. The tide was taking me away so I quickly dropped the anchor.

I checked for spark and nothing, it has Thunderbolt-V (edit: it's actually thunderbolt IV ignition!) and I have no diagnostic tools.

After getting towed back to a dock, I was able to start the engine for about 1 or 2 seconds, then it died again, no spark.

This has been an otherwise very reliable engine and I'd like to hear what you all think...

The fact that it started briefly, then lost spark again leads me to believe it's not wiring and is related to a component. This leads me to three possibilities, coil, ignition module, or distributor.

I'd like to think it's the coil.. What is the most likely culprit and is there a replacement automotive coil I can get temporarily to see if that's the issue without causing a problem since it's a marine application?

Also is it common for these barrel style coils to go bad? In automotive applications, they rarely go bad, I don't know about boats.

Thanks for all the help in advance. I'm stuck here with the boat until I can get it running.

 

[Fun Times]

Hi there, sorry to hear your down in the water. Without a test light or/and a meter, your in the guessing game at this point.

Since you had a bit of spark and lost it quickly, my first guess would be a bad coil. You'll still want to wiggle some wires around carefully just to be sure it's not the problem. I'd check the main wire harness cannon plug at the engine.

Also if you can, you could try disconnecting the gray wire at the tachometer. If it's shorted out, it will kill the spark. Check for excessive heat at the coil. Yes you can use/buy one from an auto store.

A defective ignition sensor under the dizzy cap will kill the ignition and there is a test for that in the service manual. Maybe someone can post up the ignition test tree for you. Item number 6 is your ignition sensor.
http://www.mercruiserparts.com/Show_...ION+COMPONENTS

If you get a test light and a meter, this may help.
http://www.ehow.com/how_5485497_test...ol-module.html

Hope you get it figured out soon, be safe and good luck.

 

[500dollar744ti]

Went to go work on it this morning and of course it started right up and ran until I turned it off. Then I started it again and there was no problem. I'm going to replace the coil, I don't want to be stranded if I try to get underway again.

Also made a mistake in original post, it's thunderbolt IV ignition

 

[500dollar744ti]

What is more likely to cause a problem when hot but then work when the engine has sat overnight and cooled? Coil or distributor sensor?

 

[Eric 3.7LX Alpha 1]

Here are the troubleshooting charts for both the TB 4 and TB 5 as posted by DonS:

http://forums.iboats.com/forum/engi...es-outdrives/529121-thunderbolt-ignition-test

I would print the correct one out, and have the necessary troubleshooting tools to diagnosis it WHILE your on the water. It's not acting up now, you know when it IS going to act up, so you can be ready for it when it does.

 

[stonyloam]

. The fact that it started briefly, then lost spark again leads me to believe it's not wiring and is related .........

That and the rest of what you have said leads me to think it IS wiring related. Components usually don't fail then start working again, loose or corroded wires do.

 

[grady86]

I just recently had to replace my ignition coil. I was having similar symptoms. One way I was able to finally narrow it down to the coil was by starting my troubleshooting at the spark plugs and working my way back. Once I realized that I was getting weak to no spark from the ignition coil when I tried to ground it out to the engine, I took resistance readings across the primary and secondary windings. The secondary windings were about 1000 ohms off of what they should have been. Good luck!

 

[500dollar744ti]

That and the rest of what you have said leads me to think it IS wiring related. Components usually don't fail then start working again, loose or corroded wires do.

I went over the wiring again and nothing looks suspect. I replaced the coil today and though it does run, I am not taking it out until I have the ignition sensor in the distributor replaced. I ordered the distributor hall effect sensor and it will be in Tuesday morning. I don't want to have to get towed in again so I'm going to wait to try the boat until then.

 

[thumpar]

Just throwing this out there. Do you have a lanyard switch?

 

[Villain lll]

What is more likely to cause a problem when hot but then work when the engine has sat overnight and cooled? Coil or distributor sensor?

Neither. Coils either work or don't. You won't find them to be intermittent unless the contact points are corroded. Pull your main connector apart on the front starboard side of your engine and clean, coat with dielectric/silicone Grease and re-connect. Before chasing with new parts, clean and check connections first. Good luck.

 

[500dollar744ti]

^^^I'll go look at the main engine connector now.

Just throwing this out there. Do you have a lanyard switch?

I do not, the only type of kill switch there is the shift interrupter which I checked it is working.

 

[500dollar744ti]

I installed the distributor sensor and coil and took it out for a run. It stalled again on me so I tried to figure out what I was doing different that could be making an issue.

I don't normally run at 1800-2000 no-wake speed except in this extremely heavy tidal current when I'm at the beach. After stalling again I threw out my anchor before I was nearly pushed into the drawbridge supports. The anchor finally caught and was a close call. I was just about to phone for a tow boat again when I tried it and the engine started. I feared another stall so I dragged my anchor at a very slow speed away from the bridge. At a safe enough distance, I pulled up the anchor.

This time I kept all my no-wake engine speed under 1500 rpm. I rode around for an hour doing this with no issue. I got up on plane, tried 2500-3000 slow planing without issue, I did some medium speed planing 3000+rpm and some WOT running at 4400rpm, no issues.

I ran the boat all day long without issue, keeping the no-wake rpm below 1500. It seems that as long as I do that, it won't stall.

What could cause that? Maybe the ignition module (on the riser) is overheating at a certain load range? Loosing ground after getting hot?

I'm going to try and find a used ignition module to replace it with, would relocating the grounds from the riser to somewhere else help?

 

[wellcraft-classic210]

These sort of intermittent problems can be tough to find.

(assuming you can recreate the problem in a less hazardous area) You may want to do the tests recommended in the manual with a Multi meter to nail this down. If your not familiar with multimeter usage you may want to getting someone who is to help . 2 heads are better than 1- Sometimes -- Their could be a marriage joke here. :lol:


Possible causes would be a component that such as a coil or ignition module etc that fails when heated -- this is attributed to expansion of the parts and a resulting open or short CKT. Wiring connections can cause this also & are often driven by vibration and may seem random.

Part swapping could be 1 way to resolve the issue but can get expensive.

Some of the thunderbolt ignitons would not work well with an automotive coil as auto coils overheat.

If its cutting out when you shift into or out of gear check into the shift interrupt ckt.

Good luck.

 

[Maclin]

Wondering if it is really RPM related or more throttle-position related....kind of aiming back at the shift interruptor switch or adjustments...

 

[dannys2004glastron175mx]

Your Tach mite be shorting out and killing your coil . On hook the sending wire on your Tach and go for a sail

 

[Scott Danforth]

you may need a new trigger assembly in the distributor

 

[Bondo]

you may need a new trigger assembly in the distributor

Ayuh,........ He already replaced it,......... I'd pull the motor to hull cannon plug apart, 'n look for corrosion in the wirin' connections,...........Tide = Saltwater = Corrosion,......

 

[500dollar744ti]

I went out again, all day with no problems.

I checked the cannon plug the other day and greased it, didn't look suspect. I also tried wiggling it and pulling it in and out a little with the engine idling, no stall.

I might do what was suggested about trying to make it stall in less hazardous place, if I can get it to happen somewhere I can do a little diagnostics, I might find something.